Energy
absorbed
foot- pounds



March 23, 3%? L. a. MANDICH 3,310,441

STEEL Filed July 20, 1966 7 Sheets-Sheet 2 NORMALIZED ENERGY ABSORBED FOOT- POUNDS -25 +25 +50 +70 TEMPERATURE 1 I l I I l 9 1" GAGE QUENCHED a TEMPERED 8O mm 7777/ /////LONGITUD1NAL 7c L4 I so ENERGY AssgaEn 50 FOOT-POUNDS \X 4O W TRANVER5E fi 2o g IO TEMPERATURE F INVENTOR LOU/S .Z'. MAND/CH ATTORNEYS March LL21, E97 MANDICH 3,310,441

STEEL Filed July 20, 1966 v Sheets-Sheet s NORMALIZED V-NOTCH ENERGY ABSC H:BED

FOOT- POUNDS I KEYHOLE TEMPERA FzgJS 8/2" GAGE QUENCHED 8 TEMPERED V-NOTCH ENERGY ABSQEBED FOOT POUNDS TEMPERATURE "F INVENTOR LOU/S I. MAND/CH ATTORNEYS March 2i, 1967 L. a. MANDHCH 393109441 STEEL Filed July 20, 1966 7 Sheets-Sheet 4 .1." GAGE NORMALIZED 80 V NOICH -we -75 -50 +50 +7'o 0 TEM PERATURE "F i" GAGE QUENCHED B TEMPERED v- NOTCH ENERGY ABSORBED FOOT Eouwos KEYHol-E INVENTOR F 1 -&

LOU/S I MAND/CH We, 777m? ATTORNEY 3,310,441 STEEL Louis ll. Mandieh, Kennett Square, Pm, assignor to Lukens Steel Company, Coatesville, Pa, a corporation of Pennsylvania Filed July 20, 1966, Ser. No. 569,553 23 Claims. (Cl. 1455-36) This application is a continuation-in-part of application Ser. No. 293,576, filed July 3, 1963, now abandoned, and of application Ser. No. 502,783, filed Oct. 21, 1965, now abandoned, which is a continuation-in-part of application Ser. No. 376,318, filed June 19, 1964, now abandoned.

The inventive concepts of the application relate to improvements in carbon steel. In particular, they relate to a heat-treated carbon-manganese-silicon steel of flange and firebox quality with improved notch toughness at sub-zero temperatures, and to heat-treated steel plate having high strength and notch toughness characteristics under both normal and low temperature conditions.

Steel is considered to be carbon steel when no minimum content is specified or required for aluminum, boron, chromium, cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium, or any other element added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, copper 0.60, and silicon 0.60.

In carbon steels made from raw materials including scrap steel, small quantities of certain residual elements such as copper, nickel, molybdenum and chromium are retained. These elements have been viewed as harmful but not unduly troublesome in low amounts. However, it has been found that if the levels of such residual elements are controlled, a beneficial result may be obtained.

Heretofore, 0.25 maximum percent carbon steel plates as well as other high quality carbon steel plates have not been characterized by high notch toughness at sub-zero temperatures such as prevail with the storage of liquified ammonia, liquified petroleum gases, and the like, or otherwise by having very high notch toughness at low temperatures or as possessing favorable Brinell hardness qualities.

Accordingly, it is an object of the invention to provide steel in the carbon steel category which has good low temperature impact properties and which can be made into heat-treated plate having high tensile and yield strengths and excellent notch toughness over a broad temperature range including very low temperatures. It is a further object to provide a high strength carbon steel of such type which is readily weldable. Another object of the invention is to provide carbon steel plates with the aforementioned improved qualities in thicknesses up to two inches. A still further object of the invention is to provide steel in the carbon steel category which can be made into plate havin excellent Brinell hardness qualities. A yet further object of the invention is to provide steel plates of the carbon steel category with the above indicated qualities which can be largely produced from less expensive scrap steel in a melting furnace by the mold charging process.

Other objects, adaptabilities and capabilities will appear nited States l atent O as the description progresses, reference being had to the accompanying drawings, in which:

FIGURES 1 through 8 are graphs, the ordinates of which show the impact properties of the carbon steel of the invention in energy absorbed in foot-pounds in temperature ranges of 100 to +70 F. for gauges of one inch and less of Table II;

FIGURES 911 are graphs illustrating the notch toughness characteristics of the one-inch plate No. 5 of Table VIII;

FIGURES 12-14 are graphs illustrating the notch toughness characteristics of the two-inch plate N0. 6 of Table IX; and

FIGURE 15 is a graph illustrating the notch toughness of plates having different aluminum contents before and after stress relief treatment.

It has been discovered that the unusual properties of carbon steels according to the invention can be achieved by balancing the carbon and manganese levels and the inclusion of high levels of nickel, chromium, molybdenum and copper within industrial standards of maximum for residual elements through the careful control of scrap added to the furnace producing the steel. The relative amounts of carbon and manganese have a known effect on the low temperature impact properties, yield point, tensile strength, ductility, and the like, which is significantly affected and generally improved by the inclusion of residuals as taught herein. For example, it is believed that for steels within the ambit of this invention, the efiect of molybdenum to increase the yield strength is approximately four times that of manganese, whereas the effect of chromium on the tensile strength exceeds that of the manganese. It is further thought that the improved toughness results from the residual nickel content and the circumstance that the residuals, particularly the chromium and molybdenum, permit a higher manganese-carbon ratio which, in turn, contributes to the resulting high notch toughness.

Steel in accordance with the invention is prepared in a melting furnace of the open hearth or electric arc type. Approximately eighty percent or more of the charge is scrap steel with about one half of same being purchased scrap and the remainder being scrap generated at the mill, from trimmings, diversions, etc. It is important that the chemical constituents of such scrap be known as accurately as possible. By experience it has been learned that the copper, nickel, chromium and molybdenum contents of purchased scrap fall in a ratio of roughly 7 to 5 to 3 to 1, respectively. Thus, by careful control of scrap in accordance with one of the chemical constituents-say copper, the other constituents are also controlled within limits. The purchased scrap is first carefully inspected and chemically checked by individuals skilled in this art for segregation into identified areas of the mills scrap yards. Scrap generated at the mill is similarly identified and segregated. At the present time, with such close inspection and segregation directed primarily to the copper content, steel having characteristics in accordance with the invention may be produced with less than five percent diversions.

By controlling the type and amount of scrap, included in the melt, the level of copper, nickel, chromium and molybdenum contents are similarly controlled. With TAB LE I Source Percentages Molds 1 No. 1 Bundles No. 2 Heavy Melting Pit (Sprues and Runners) Total Plant Scrap The foregoing produced steel which included 30% copper, .19% nickel, .13% chromium and .04% molybdenum. The cost of a comparable charge of pig iron with the elements of copper, nickel, chromium, and molybdenurn added in such percentages, is approximately two and one half times the cost of the mixture set forth above.

Heat-treated steel plates according to the present inventive concepts include several species. One chemistry which combines strength with excellent impact properties offers in its normalized condition a tensile strength range of about 70,00090,000 p.s.i. and a yield point of about 50,000 p.s.i., and in a quenched condition a tensile strength range of about 80,000100,000 p.s.i. and a minimum yield strength of about 60,000 p.s.i. Another species with a higher minimum amount of manganese is designed to be used in applications where very high strength is required and where excellent notch toughness at low temperatures is requisite. A further heat-treated steel is designed for plates that must also possess the above qualities to a considerable degree as well as superior hardness properties.

Considering the first indicated species, a scrap mixture charge of the type previously set forth is melted. In general, and contrary to the usual practice, a high total of copper, nickel, chromium, and molybdenum within admissible industrial limits is sought. Charged into the melting furnace just prior to the tap or into the ladle is standard ferromanganese or other manganese additive whereby the manganese percentage by weight will be 0.70 to 1.35 and preferably 1.00 to 1.25. With the chromium and molybdenum content on the high side, the manganese and the carbon in particular need not be so high. At the time the manganese is added, ferrosilicon or another silicon-containing additive is added to the melt to deoxidize and quiet the molten steel.

Aluminum is added to the metal in amount sufiicient to produce a fine grain structure. It has been found that 0.015 to 0.055 percentage aluminum by weight is sufficient for this purpose. However, additions of 0.070 appear to enhance the notch toughness still further in the lower temperature ranges.

In the cold-charging production of steel, the charges are maintained in a heated or molten condition for approximately twice to four times as long for a given tonnage than with the hot charge method. During the molten period, the carbon content tends to decrease. It has been found that less carbon is required for strength in the thinner gauges than in the thicker gauges. For this reason, different ranges of carbon in percentage by weight are specified for different gauges of plate approximately as shown in the following table:

i TABLE II Gauge: Carbon range A .10.12 A" .11.l3 /2" .12-.14 /8" .13-.15 A." .14-.16 1" .15-.17 1 /2" and over .16.20

The chromium content also tends to become lower while the steel is molten and for this reason, a slightly high chromium content in the initial charge is not considered deleterious.

The specific chemistry of the resulting carbon steel is in ranges about as follows:

TABLE III Element: Percentage by Weight Carbon 0.08 to 0.25 Manganese 0.70 to 1.35 Phosphorus 0.010 to 0.035 Sulphur 0.010 to 0.040 Silicon 0.10 to 0.35 Aluminum minimum 0.015 Copper 0.01 to 0.47 Nickel 0.05 to 0.35 Chromium 0.05 to 0.25 Molybdenum 0.01 to 0.15 Iron and incidental impurities Balance It is to be understood that the carbon content is preferably in the ranges indicated in Table II, depending upon the gauge of the plates. The manganese range is preferably held between 1.00 to 1.25 percentage by weight. The aluminum should be sufficient to obtain a fine grain steel. As noted before, the addition of 0.070 aluminum by weight percentage improves notch toughness at the lower temperatures, but generally 0.015 to 0.055 aluminum is sufiicient.

The foregoing steel is prepared in plate or head forms in thicknesses from to 2", which are then treated by normalizing or by quenching and tempering. Normalizing is accomplished by heating the head or plate uniformly to an austenitizing temperature, generally 1625l675 F., and holding same at the temperature for one hour per inch thickness, followed by air cooling. Quenching and tempering consist of the same treatment except in stead of cooling by air, the plate or head is quenched in water, then heated uniformly to a tempering temperature, generally 1175-1250 F., which is held one hour per inch of thickness, followed by air cooling.

Carbon steel plate produced in accordance with the above disclosure has properties heretofore only attainable in low alloy steels containing vanadium, columbium, nitrogen, or combinations thereof, and fully alloy steels as classified by AISI standards. These unusual properties are as set forth in Table IV.

In carbon steels, it is common for purchasers to specify a certain maximum or minimum copper content. For example, a maximum copper content of 0.25% or 0.35% may be specified, or a request for a minimum of 0.20% is usual. It is known that the inclusion of copper in amounts from 0.200.60% increases the resistance of the steel to atmospheric corrosion and slightly increases the yield point and tensile strength, but adversely affects the ductility. In filing orders with controlled production as disclosed herein, averages and range variations of the copper, nickel, chromium and molybdenum are obtainable as disclosed in the following table:

Steel No. 3 for longitudinally oriented specimens by standard Charpy V-Notch tests and keyhole specimens as defined in ASTM standards. FIGURES 6, 7 and 8 are similar graphs for Steels Nos. 4, 9, and 10, respectively.

From Table V, it will be noted that the heats requiring the 0.20% min, and 0.35% max. copper contained average totals of 0.687% and 0.660% of the four elements, respectively, whereas the heats requiring the 0.25% max. copper had an average total of 0.502%. The level of such elements in the former heats is sufiicient to improve significantly the physical properties of steel according to the invention. However, while the level of the latter heat also definitely improves the physical properties of the steel, the improvement is less than with the former. With higher levels, the manganese range of the steel may, if desired, be reduced to be within a range of 0.70 to 1.10 percent by weight, but with lower levels, a range of 1.00 to 1.35 percent by weight of manganese is preferable to obtain the desired physical characteristics of the steel. In the same manner, the carbon content may be maintained in the lower or upper limits inversely to the level of the elements copper, nickel, chromium and molybdenum, particularly the levels of the latter two elements.

Specific examples of the chemistries together with the physical characteristics of carbon steel plates which come within the scope of the invention are shown in the following table:

The above disclosed carbon steels are readily Weldable. For most applications, low hydrogen electrodes are preferable. When the plates are to be used in low temperature service, the impact properties of the joint are important. It has been found that a nickel-bearing electrode, such as AWS E8018Cl for Steel N0. 9 and AWS E80l6-Cl for Steels Nos. 5 and 6, gives satisfactory results. With submerged arc welding techniques, welds with good toughness may be obtained with carbonmanganese-nickel wire and fluxes especially developed to provide notch tough welds. A weld metal as disclosed in U.S. Patent No. 3,110,798 to Louis K. Keay, of Nov. 12, 1963, may also be employed with good results. Excessive heat input during welding is to be avoided.

The following heat-treated carbon steel plates are designed to be used Where very high strength is required and Where excellent notch toughness at low temperatures is requisite, and include heat treated steel plates having, in addition to a considerable degree of such qualities, superior hardness properties.

All of these heat-treated steel plates are quenched in the vicinity of l5501750 F. and tempered at temperatures above about 600 F. Plates made of the very TABLE VI Steel No C Mn P S I Si Al Cu Ni Cr M0 116 016 .019 .26 032 15 11 09 01 1. 24 010 021 23 017 16 08 03 1. 34 012 026 22 .020 l8 3O 02 1. 32 018 028 23 015 18 1O 21 01 1. 34 012 025 27 028 28 .16 07 01 1.17 013 026 25 019 21 11 08 01 1. 32 013 020 25 030 16 10 08 01 1. 016 O16 22 034 15 11 .10 02 1. .012 015 23 .025 17 .16 07 01 1. 18 011 018 24 034 12 08 05 01 1. 013 028 27 035 33 15 08 .01 1.35 012 015 26 046 l8 10 07 01 Percent Yield Yield Tensile Elong. Percent Steel No. Plate Heat Treatment Point, Strength, Strength, Red, Gage p.s.i p.s.i. p.s.i. Area V Normalized 54, 200 17, 250 26 62 quenched and Tempered 65, 000 84, 300 30 Normalized 55, 350 78, 950 27 63 Quenched and Tempered 64 100 84, 200 26 67 Normalized. 73, 400 29 65 Quenched an 83, 700 27 66 Normalized 16, 400 27 62 3.1 quenched and Tempered. 82, 450 28 64 1 Normalized 51, 000 73, 200 26 63 1 Quenched and Tempered. 63, 000 83, 200 27 63 2 Normalized 50, 800 69, 800 25 64 2 Quenched and Tempered. 58, 200 79, 300 28 65 FIGURE 1 is a graph showing a typical transition curve for the impact properties of Steel No. 5 by standard Charpy V-Notch tests within the shaded areas. FIG- URES 2, 3, and 4 are similar graphs for Steels 6, 9, and 10, respectively. FIGURE 5 is a graph showing a typical transition curve of the impact properties of 70 high strength steels have the characteristics shown in Tables VIII and IX and are tempered at temperatures above about 950 F., preferably about ll00l300 F. Plates made of steels having desirable hardness characteristics are characterized as reported in Table X and are tempered at lower temperatures, preferably 650-700 F.

8 carbon silicon steels for boilers and pressure vessels. The steel plates of Table VIH can be made to a fine grain practice and yet have a specification of 70,000 p.s.i.

TABLE VII Element: Percentage y Weight minimum yield strength and 85,000 p.s.i. minimum tensile Carbon to 025 strength. Moreover, these plates, being made chiefly from g i scrap, are produced for relatively little cost.

As shown in FIGURES 9-11, the longitudinal and m 658 transverse V-notch impact transition tests demonstrate S1l1con 0.1 to 0.35 Copper 01 to 0 4 that the plates of Table VIII possess excellent notch Nickel b 10 toughness. Measurements were made by the standard Chromium I (m5 to 025 Charpy V-Notch impact tests. The transition curves Molybdenum 001 to shown in FIGURES 9, 10, and 11 illustrate: 1) foot- Aluminum 0.005 to 0.1 pounds energy absorbed; (2) percent fibrous fracture; and

TABLE VIII Heat Treatment Plate F. Yield Tensile Percent Percent Gage 0 Mn P S Si Cu Ni Cr Mo Al Str. Str. Elong. e

' (K s.i.) (K ;=.i in 2 Area Quench Temper 1 1,050 1,200 .15 1.54 .010 .028 .18 .20 .15 .08 .03 .055 ,{1 gig 33:2 23:1

0 1 1,050 1,100 .19 1.50 .014 .015 .27 .20 .17 .07 .04 .057 Iii The chief reason for the excellent qualities of the steel (3) mils lateral expansion of the broken impact speciplates with the above chemistries can be attributed to men. These curves are typical of the results obtained the balancing of elements within the limits disclosed in for the other steel plates of Table VIII in that the longi- Tables VIII, IX, and X. The amounts and ratios of 35 tu-dinal (L) values and the transverse (T) values are near carbon and manganese together with the levels of the or above foot-pounds at ambient temperatures and deresidual elements have a dramatic effect on the tensile crease to 20-30 foot-pounds .at about or F.

and yield strengths as Well as the toughness of these plates. before further decreasing at an accelerated rate. The L Control of the amounts of oxidation resistant elements values for No. 6 steel plate, however, were considerably is most satisfactorily achieved through scrap added to the 40 higher (about 100 foot-pounds) at ambient and lower charge in the furnace. The low temperature properties temperatures until these values fell more rapidly at about are further enhanced by the addition of aluminum. Fur- 60 to 70 F.

ther improvement results when the steel contains relatively It has been found that the steels of Table VIII have a high levels of copper, nickel, chromium and molybdenum minimum Charpy V-Notch impact strength of 20 footwithin the residual limits acceptable by industrial stand- 4r pounds at F. and 15 foot-pounds at 100 F.

ads for carbon steels, the theory to explain such im- 0 Table IX shows the strength characteristics of steel provement being as previously set forth. As previously plate having about the same chemical make-up as those in disclosed, it is possible to meet these parameters using Table VIII except that the plates are produced to coarse or more scrap in the furnace charge with attending grain practice. This change in deoxidation practice pereconomic advantages in view of present scrap prices. 50 mits higher strengths to be obtained. In fact, the steel Table VIII is illustrative of the high yield and tensile plates of Table IX can be made to 80,000 psi. minimum strengths obtainable for plates made according to fire grain yield strength and 95,000 to 100,000 minimum tensile practice. strength. Although these high values are characteristic In the steel making field, the higher grades of Carbon of alloy steels, they are obtainable in relatively inexpensteel can be made to mechanical specifications. Howsive carbon steels according to the present invention.

TABLE IX 1; Percent m Heat ment Yield Tensile Elong. Percent Gage, 0 Mn P s Si Cu Ni Cr Mo Al s11. Str. (K s.i.) (K st) Area Quench Temper 5 2 1,050 1,200 .20 1.55 .008 .021 .23 .19 .11 .05 .02 .010 88:; ig g i; 2g}

ever, only a few of the highest grade carbon steels can be made to a minimum tensile strength of 75,000 psi.

FIGURES l2, l3, and 14 show transition curves of the No. 6 plate of Table IX. While the toughness of the An example of the latter grade steels is the best firebox 75 steel plates of this table is not as outstanding as those 329 of Table VIII, the toughness is surprisingly good considering the strength levels involved.

As shown in FIGURE 12, when foot-pounds absorbed is plotted in standard Charpy V-l otch impact tests against In the specification and claims all percentages are by weight and temperatures are given in Fahrenheit unless expressed to the contrary. The term plate is intended to cover heads and the like.

temperature, the value is less than 40 foot-pounds at While a number of specific examples of the invention ambient temperatures but generally more than 20 foothave been set forth in the foregoing description, no unpounds. The foot-pound values fall off for both L and necessary limitations should be understood therefrom for '1 measurements so that the decline of the curves have numerous modifications will be obvious to those skilled almost leveled ofif at 60 to 70 F. Similarly, the in the art within the scope of the invention. other values for percent fibrous fracture and mils lateral Having thus described my invention, what I claim as expansion are correspondingly lower as seen in FIGURES new and desire to secure by Letters Patent of the United 13 and 14. It has been found that minimum longitudinal States is: Charpy V-Notch values of 15 foot-pounds can be met at 1. A high strength steel plate containing iron, incidental 10 F. in 2-inch plates, at F. in l-inch plates, and impurities and about: at F. in Az-inch plates. 15

Table X refers to the chemistry and hardness charac- Element: Percentage by weight teristics of a rolled plate made from steel that has been Carbon 0.08 to 0.25 heat-treated but tempered at a temperature between about Manganese 0.70 to 1.35 600 to 950 F. The chemistry of the steel plates of Phosphorus up to 0.035 Table X have a higher carbon maximum limit, namely, 20 Sulphur up to 0.040 about 0.3%, and a lower manganese content, about 1.1- Silicon 0.10 to 0.35 1.4%, than the other plates described in Tables VIII and Aluminum minimum 0.015 1X. The use of up to 0.1% aluminum is optional but Copper 0.01 to 0.47 preferred and the plates can be made to a minimum Nickel 0.05 to 0.35 Brinell hardness of 320 BHN for fine grain grade steel 25 Chromium 0.05 to 0.25 and of 350 BHN for coarse grain grade steel. Molybdenum 0.01 to 0.15

TABLE X Heat Treatment, Brinell Hardness Plate Gage, (3 Mn P 3 s1 Cu Ni 01' Mo Al Top Bottom Quench Temper End End 1,650 351 321 94, 1,650 364 364 1,650 321 340 1,650 302 351 i 1, 332 32 16 1 50 340 340 1 50 351 304 96 1,650 340 351 ;g 1,650 337 337 9/, 1,650 364 387 A 1,650 364 337 a; 1,650 321 364 FIGURE 15 shows the effect of stress-relief treatment on steels having 80,000 p.s.i. yield strength which are tempered at temperatures above 950 F. A significant finding is that these steels do not become embrittled as a result of stress-relief treatment if the aluminum content is maintained within the range of about 0015-003 percent, preferably about 0.02%.

The first steel at the top of the graph showing improvement with reference to the emhrittlement efiect was a /3" gauge plate in a full size test having 0.025 percent aluminum content. The second steel at the bottom of the graph was a gauge in a 4 size test containing 0.01 aluminum content. The standard Charpy V-Notch tests were conducted in a longitudinal direction per ASTM Standard E 2364. Other details are set forth in the following table.

TABLE XI First Steel, Second Steel, Elements Percentage by Percentage by Weight Weight water quenched at about 1,650" F.; air cooled at about 1,100 F.; stress-relief treatment at about l,050 F.; furnace cooled.

2 Water quenched at about 1,550 F.; air cooled at about 1,200 F.; stress-relief treatment at about 1,075 F.; air cooled.

said steel plate being in a heat-treated condition and characterized by a yield point in excess of about 50,000 psi, a tensile strength in excess of about 70,000 psi, and a minimum Charpy V-Notch impact strength at 75 F. of 15 foot-pounds.

2.. A high strength steel plate according to claim 1 wherein said heat treatment comprises normalizing said plate by heating to an austenitizing temperature and holding said temperature for about one hour per inch thickness, followed by cooling.

3. A high strength carbon steel plate according to claim 2 wherein said austenitizing temperature is 1625- 1675 F., and said cooling is air cooling.

4. A high strength steel plate according to claim 1, wherein the copper, nickel, chromium, and molybdenum content ranges are 0.26 to 0.42, 0.14 to 0.33, 0.04 to 0.22, and 0.024 to 0.080, percentage by weight, respectively, and the manganese content range is 0.70 to 1.10 percentage by weight.

5. A hi h strength steel plate according to claim 1, wherein the copper, nickel, chromium and molybdenum content ranges are 0.24 to 0.47, 0.14 to 0.32, 0.07 to 0.23, and 0.022 to 0.080 percentage by weight, respectively, and the manganese content is 0.70 to 1.10 percentage by weight.

6. A high strength carbon steel plate according to claim 1, wherein the copper, nickel, chromium, and molybdenum content are 0.15 to 0.27, 0.11 to 0.26, 0.03 to 0.18, and 0.02 to 0.08, percentage by weight, respectively, and the manganese content range is 1.00 to 1.35 percentage by weight.

11 7. A high strength steel plate containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.08 to 0.25 Manganese 0.70 to 1.35 Phosphorus up to 0.035 Sulphur up to 0.040 Silicon 0.10 to 0.35 Aluminum minimum 0.015 Copper 0.01 to 0.47 Nickel 0.05 to 0.35 Chromium 0.05 to 0.25 Molybdenum 0.01 to 0.15

said steel plate being in a quenched and tempered condition and characterized by a yield strength in excess of about 58,000 p.s.i., a tensile strength in excess of about 79,000 p.s.i., and a minimum Charpy V-Notch impact strength at 75 F. of 15 foot-pounds.

8. A high strength steel plate in accordance with claim 7 wherein said plate is first austenitized by heating to a temperature of about 1550 F.1670 F., then quenched and then tempered at a temperature of about 1175 F.-1250 F.

9. A high strength steel plate according to claim 7, wherein the copper, nickel, chromium, and molybdenum content ranges are 0.26 to 0.42, 0.14 to 0.33, 0.04 to 0.22, and 0.024 to 0.080, percentage by weight, respectively, and the manganese content range is 0.70 to 1.10 percentage by weight.

10. A high strength steel plate according to claim 7, wherein the copper, nickel, chromium and molybdenum content ranges are 0.24 to 0.47, 0.14 to 0.32, 0.07 to 0.23, and 0.022 to 0.080 percentage by weight, respectively, and the manganese content is 0.70 to 1.10 percentage by weight.

11. A high strength carbon steel plate according to claim 7, wherein the copper, nickel, chromium, and molybdenum content are 0.15 to 0.27, 0.11 to 0.26, 0.03 to 0.18, and 0.02 to 0.08, percentage by weight, respectively, and the manganese content range is 1.00 to 1.35 percentage by weight.

12. A fine grain quenched and tempered high strength steel plate containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.15 to 0.4 Manganese 1.1 to 1.65 Phosphorus less than 0.04 Sulphur less than 0.04 Silicon 0.1 to 0.6 Aluminum minimum 0.015 Copper 0.1 to 0.6 Nickel 0.05 to 0.35 Chromium 0.05 to 0.25 Molybdenum 0.01 to 0.15

said steel plate being characterized by a yield strength in excess of about 70,000 p.s.i., a tensile strength in excess of about 85,000 p.s.i., and a minimum Charpy V-Notch impact strength at -75 F. of 15 foot-pounds.

13. A fine grain quenched and tempered high strength steel plate containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.15 to 0.25 Managanese 1.4 to 1.65 Phosphorus less than 0.04 Sulphur less than 0.04 Silicon 0.1 to 0.6 Aluminum minimum 0.015 Copper 0.1 to 0.6 Nickel 0.1 to 0.35 Chromium 0.05 to 0.25

Molybdenum 0.02 to 0.15

said steel plate being characterized by a yield strength in excess of about 70,000 p.s.i., a tensile strength in excess of about 85,000 p.s.i., and a minimum Charpy V-Notch impact strength at F. of 20 foot-pounds.

14. A steel plate in accordance with claim 13 which was tempered above about 950 F.

15. A coarse grain quenched and tempered high strength steel plate containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.15 to 0.4 Manganese 1.1 to 1.65 Phosphorus less than 0.04 Sulphur less than 0.04 Silicon 0.1 to 0.6 Aluminum maximum 0.1 Copper 0.1 to 0.6 Nickel 0.05 to 0.35 Chromium 0.05 to 0.15 Molybdenum 0.01 to 0.1

said steel being characterized by a yield strength in excess of about 80,000 p.s.i., a tensile strength in excess of about 95,000 p.s.i. and a minimum Charpy V-Notch impact strength at 10 F. of 15 foot-pounds.

16. A coarse grain quenched and tempered high strength steel plate containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.2 to 0.3 Manganese 1.3 to 1.65 Phosphorus less than 0.04 Sulphur less than 0.04 Silicon 0.1 to 0.6 Aluminum maximum 0.05 Copper 0.1 to 0.6 Nickel 0.1 to 0.35 Chromium 0.05 to 0.25 Molybdenum 0.02 to 0.15

said steel being characterized by a yield strength in excess of about 80,000 p.s.i., a tensile strength in excess of about 95,000 p.s.i., and a minimum Charpy V-Notch impact strength at 10 F. of 15 foot-pounds.

17. A steel plate in accordance with claim 16 which was tempered above about 950 F.

18. A heat-treated steel plate tempered at a temperature between 600 and 950 F. containing iron, incidental impurities and about:

hardness of at least 320 BHN.

19. A heat-treated steel plate tempered at a temperature above 950 F. containing iron, incidental impurities and about:

Element: Percentage by weight Carbon 0.15 to 0.25 Manganese 1.3 to 1.65 Phosphorus less than 0.04 Sulphur less than 0.04 Silicon 0.1 to 0.6

Aluminum 0.005 to 0.1 Copper 0.1 to 0.6 Nickel 0.05 to 0.35 Chromium 0.05 to 0.25 Molybdenum 0.01 to 0.15

said steel being characterized by a yield strength in excess of about 70,000 p.s.i., a tensile strength in excess of about 85,000 p.s.i., and a minimum Charpy V-Notch impact strength at 10 F. of 15 foot-pounds.

20. A steel plate in accordance with claim 19 having a yield strength of at least 80,000 p.s.i. and a tensile strength of at least 95,000 psi.

21. A steel plate in accordance with claim 19 having a minimum Charpy VNotch impact strength at -lOO F. of 15 foot-pounds.

22. A steel plate in accordance with claim 19 having a minimum Charpy V-Notch impact strength at -20 F. of 15 foot-pounds.

23. A steel plate in accordance With claim 19 having a yield strength of at least 80,000 p.s.i. and which is resistant to stress-relieving embrittlement.

114 References Cited by the Examiner FOREIGN PATENTS 11/1958 Great Britain.

OTHER REFERENCES Metals Handbook, 8th edition, vol. 1, published by SM, 1961, Cleveland, Ohio, relied on pages 8791 and 16 DAVID L. RECK, Primary Examiner.

C. N. I VELL, Assistant Examiner. 

1. A HIGH STRENGTH STEEL PLATE CONTAINING IRON, INCIDENTAL IMPURITIES AND ABOUT: 